In the manufacture of hard disks for computer memories, substrates are carried into a vacuum environment where various processes are performed and where various layers are deposited onto the surfaces of the substrates. The various process steps may include for example heating the substrate, cooling the substrate, sputter coating layers onto the substrate, laying down layers using chemical vapor deposition and enhanced plasma techniques, depositing protective carbon layers on the substrate, and other like processing steps. In some instances the disk manufacturer also places a lubricant onto the final surfaces of the disk.
During the course of the described manufacturing processes, a substrate is typically held along its edges and is moved into a processing chamber where the disk is simultaneously processed on both sides of the substrate. At least following deposition of the magnetic layers and prior to the deposition of the final layers, one of which will generally comprise a carbon layer, it is generally necessary to cool the substrate and to do so very quickly. In the prior art, as exemplified by U.S. Pat. No. 5,215,420, processing stations are positioned to surround a central vacuum area. A cassette of substrates moves into the loading area of the system and then into the central area where individual disks are lifted from cassettes and carried into the system where they move sequentially through various process stations that surround the central area. A lifter holds the disk by its edges and carries the disk from station to station until the disk has been processed at all stations at which point the disk is returned to a cassette and removed from the system. One or more of the stations surrounding the central area of this type equipment is a cooling station. Such a station may appear more than once in the sequence of manufacturing a finished memory disk. Cooling, in the prior art described, has been performed by gas conduction by positioning a disk to be cooled between heat sinks, closing the cooling compartment to separate it from other compartments and from the central area of the system. A gas is then added to the closed compartment which changes the pressure in the cooling compartment by raising it toward atmospheric and to a preferred pressure for heat transfer by gas conductivity. This facilitates the transfer of heat from the disk to the heat sinks or cooling plates positioned on each side of the disk within the compartment. Gases typically used for this purpose are helium and hydrogen and mixes of the two because these gases provide good thermal conductivity for heat transfer. Generally the pressure is raised until it reaches to within about of 10 to 15 torr. While the pressure in the compartment is raised the pressure outside the compartment remains at a lower vacuum pressure of about 10−7 torr. A station, as described, is the subject of U.S. Pat. No. 5,181,556, and a system including cooling stations as described has been and currently is available commercially from Intevac, Inc. of Santa Clara, Calif. and is also sold incorporated into the Intevac's MDP 250. Noteworthy is that the system is one in which substrates are carried from station to station and are subjected to processing at each station simultaneously and during the same time interval. Although systems can operate differently, this approach has been generally accepted in the field since it is most efficient in the production of large quantities of commercially acceptable finished disks. Thus if less time were required to cool a substrate and if this lesser amount of time were adequate to perform all of the other particular operations to which the substrate is exposed the entire system would have the capability of functioning more quickly and could in a unit of time produce more finished disks. With time, commerce has demanded faster speeds from these manufacturing systems, lower costs for the manufactured disks and improved qualities in the manufactured disks including increased storage capabilities. To satisfy this need there was developed a new system which is described in pending application Ser. No. 10/361,308, filed Feb. 10, 2003. In this system the substrate is held in a slightly different manner being gripped at its edges around its circumference in a disk carrier, again however, permitting processing of both sides of the substrate. Each processing compartment is a self-contained vacuum chamber and, the holder, as in the case of the earlier units, moves from processing station to processing station where the substrate is subjected to treatment. Here too rapid cooling is an important factor. The disclosure of this pending application is incorporated herein by reference.
Heat flux leaving the substrate is proportional to ΔT/Δx, where ΔT=(Temperature of substrate)−(Temperature of cooling plate) and Δx=the gap between the substrate and cooling plate. If the cool plates are cryogenically cooled, significant improvement in the cooling rate can be difficult or impossible to achieve by increasing ΔT, but by reducing the gap, Δx, one can significantly increase the cooling rate of a substrate within a cooling station. In general, the method of transporting substrates, on support carriers that grip the edges of the substrates during transport and are continuously present during the cooling step permit processing on both sides of the substrate, but require clearance between the cooling plates for the carriers during the cooling process. Thus the gap compelled by the disk carriers has an effect on and can control cooling rates for substrates. A way to reduce the required time for cooling is to place the cooling plates closer to the substrate during the cooling process, This requires movement of the heat sinks toward and away from the substrate being cooled in order to permit movement of the substrate into and out of the cooling compartment. Without a technique of dynamically measuring the gap between the substrate and moving cooling plates, the gap is restricted by the accuracy of the placement of the substrate between the plates. In other words, if the placement of the plane of the substrate can vary in position ±ε, then the plate can not be moved any closer than ε to the substrate without risking contact. This restricts the plate from coming closer than about ˜0.100 inch in processing systems of the type now in use. However, if the plate could be placed ˜0.025 inches from the substrate, for example, one fourth the distance described in the previous sentence, four times the heat flux could be carried away from the substrate. What is of interest in this technology is to be able to work with the surfaces with a separation of less than about 0.100 inch apart and particularly with a separation in a range of from about 0.02 inches to about 0.050 inches.